Ozone is one of the most powerful oxidizers and disinfectants available. Ozone not only kills bacteria, but also inactivates many viruses, cysts and spores. In addition, ozone oxidizes many organic chemical compounds, including chloramines, soaps, oils and other wastes thereby rendering them harmless to the environment. Accordingly, ozone may be used for a number of purposes including: drinking water purification, waste water treatment, air purification and sterilization, and a variety of medical uses.
Ozone is typically generated by one of two methods. Ultraviolet lamps operating at a wavelength of between 180-190 nanometers may be used to produce ozone in ambient air. Ozone may also be generated by creating an electrical corona discharge between two energized electrodes in ambient air or in another oxygen containing gas. The electrodes are typically separated by a dielectric material, such as a glass, or an air gap separation may be provided. The corona discharge is an ionization of the air and is visually indicated by the presence of a pale violet or bluish color in the area between and surrounding the electrodes.
Because ozone has a half-life of only about 22 minutes in ambient air before dissociating back to oxygen, a process requiring ozone must have an ozone generator in close proximity to the desired point of application of the ozone. Thus, an ideal ozone generator is desirably compact, relatively simple in construction, consumes little electricity, and produces little waste heat while producing a high concentration of ozone.
A number of ozone generators have been made or proposed based on the electrical corona discharge process for producing ozone. In particular, a wide assortment of electrode configurations have been developed to try to improve the performance of the basic corona discharge ozone generator. For example, an ozone generator electrode formed from a planar wire mesh or screen is disclosed in U.S. Pat. No. 2,658,868, to Collison, which discloses in a cylindrical ozone generator wherein both the inner and outer electrodes are preferably provided by concentrically disposed wire screens separated by a dielectric tube. Similarly, U.S. Pat. No. 4,035,657 to Carlson discloses an ozone generator having concentric electrodes formed from planar rectangular sheets of stainless steel wire mesh screen.
Two U.S. Pat. to Bridge, U.S. Pat. Nos. 832,768 and 935,457, disclose a cylindrical surface electrode having openings therein permitting the flow of a gas through and transverse to the electrode. The Bridge patents teach various electrode surface configurations including a perforated tubular shape, a rectangularly perforated shape, and a wire mesh. U.S. Pat. No. 788,557 to Sahlstrom discloses planar or concentrically positioned electrodes separated by a dielectric, and wherein the electrodes have either pointed raised portions or are formed of a wire gauze.
Ozone generator electrodes having raised portions on the electrode surface have been proposed. For example, Saylor discloses, in U.S. Pat. No. 4,214,995, an ozone generator having a plurality of electrode sets, each set having a dimpled inner electrode in a sealed dielectric and surrounded by an outer electrode spaced from the inner electrode to permit a flow of air therebetween. U.S. Pat. No. 4,062,748 to Imris discloses a bipolar grid shaped electrode wherein the bipolar and discharge electrodes have surfaces with sawtooth or needle-shaped points.
Smooth or flat electrode surfaces are disclosed, for example, in U.S. Pat. Nos. 4,213,838 and 4,090,960 to Lowther and Cooper, respectively. The Lowther patent discloses a corona reaction chamber for producing ozone, wherein excess heat is carried away from the system by a gas flow therethrough, and wherein the electrodes are closely spaced flat plates. The Cooper patent discloses an apparatus with two electrodes separated by a porous sheath filter whereby ozone generated from a tubular smooth inner electrode is passed through the sheath as it is formed and injected out into a flow of liquid.
"Filled" electrodes for ozone generation have also been proposed, wherein the electrode is formed of a mass of filling material. For example, Kuhlenschmidt, in U.S. Pat. No. 1,437,760, discloses an ozone generator having a concentric series of evacuated and sealed glass structures containing each electrode. Passageways between the glass structures permit fluid flow therethrough. The Kuhlenschmidt evacuated glass structure electrodes are filled with a material, such as loosely arranged metal chips, coarse metallic fillings and wire chips, interlacingly arranged pieces of wire gauze, or leaden shot having a spherical diameter of about one millimeter.
U.S. Pat. No. 4,351,734 to Kauffman discloses an ozone generator for treating a wastebearing liquid by passing air through an electrode bed in the liquid. The Kauffman electrode bed consists of two mesh grids with a packing of aluminum shot therebetween. Castor, in U.S. Pat. No. 3,023,155, discloses a cylindrical ozone generator having an inner electrode consisting of a tube with passages for the flow of air therethrough and further surrounded by a mass of aluminum granules preferably on the order of fifty to twenty-five thousandths of an inch in size. The aluminum particles of the Castor electrode are each insulated from one another by the formation of an oxide coating thereon.
Other approaches have been proposed to modify the basic electrical corona discharge and thereby achieve greater ozone conversion efficiency and/or greater energy consumption efficiency. For example, U.S. Pat. No. 4,417,966 to Krauss et al. discloses an ozone generator having a glow discharge chamber in which an electrode is located and in which a gas, such as neon, is ionized by an electric field that is produced by a voltage pulse at a frequency of from 10-16 KHz. Thus, in Krauss the entire glow discharge chamber functions as an inner plasma electrode and the outer electrode has a net-like form. Masuda discloses, in U.S. Pat. No. 4,614,573, an ozone generator which first compresses then cools the oxygen containing gas before passing it between a pair of electrodes--the inner electrode being formed of a series of linear electrodes on the inner surface of a cylindrical dielectric tube.
Unfortunately, despite the numerous beneficial applications for ozone, there still exists a need for an ozone generator that is relatively compact, rugged, reliable, readily manufactured, energy efficient, and which produces a high concentration of ozone.